SWP Solar Wind & Interplanetary Medium 1 — Questions and Answers
Question 1: The Parker spiral describes:
- The helical path of solar energetic protons to Earth
- The Archimedean spiral shape of the interplanetary magnetic field resulting from solar rotation and radial solar wind flow (Correct answer)
- The spiral structure of solar flare ribbons
- Coronal hole rotation patterns
Correct answer: The Archimedean spiral shape of the interplanetary magnetic field resulting from solar rotation and radial solar wind flow
Eugene Parker showed that the combination of radial solar wind outflow and solar rotation at 27 days causes the IMF to trace an Archimedean (Parker) spiral from the Sun to the outer heliosphere.
Question 2: At 1 AU, the average solar wind speed is approximately:
- 100–200 km/s
- 400–500 km/s (Correct answer)
- 800–1000 km/s
- 1500–2000 km/s
Correct answer: 400–500 km/s
The ambient slow solar wind at 1 AU averages about 400–500 km/s; fast streams from coronal holes average 600–800 km/s, while CME sheaths can exceed 1000 km/s.
Question 3: A corotating interaction region (CIR) forms when:
- A CME overtakes the ambient solar wind
- A fast solar wind stream from a coronal hole runs into and compresses the slower ambient solar wind ahead of it (Correct answer)
- Two CMEs interact in the interplanetary medium
- Solar wind density doubles during solar maximum
Correct answer: A fast solar wind stream from a coronal hole runs into and compresses the slower ambient solar wind ahead of it
As the Sun rotates, a fast wind stream continually runs into the slower wind ahead, building up a compressed, dense interaction region that corotates with the Sun.
Question 4: The southward component of the interplanetary magnetic field (Bz) is critical for geomagnetic activity because:
- Southward Bz increases solar wind pressure
- Southward Bz enables magnetic reconnection at the dayside magnetopause, transferring solar wind energy into the magnetosphere (Correct answer)
- Southward Bz is associated with CME arrival at Earth
- Southward Bz directly increases radiation belt electron flux
Correct answer: Southward Bz enables magnetic reconnection at the dayside magnetopause, transferring solar wind energy into the magnetosphere
When IMF Bz is directed southward (antiparallel to Earth's northward equatorial field), dayside reconnection opens the magnetosphere, allowing solar wind momentum and energy to enter.
Question 5: The L1 Lagrange point (~1.5 million km sunward of Earth) is the preferred location for space weather monitors because:
- It has direct line-of-sight to all solar active regions
- It is gravitationally stable and provides ~15–60 minutes of advance warning before solar wind structures reach Earth (Correct answer)
- L1 is inside the magnetosphere, giving real-time magnetospheric data
- Solar wind speed is fastest at L1
Correct answer: It is gravitationally stable and provides ~15–60 minutes of advance warning before solar wind structures reach Earth
L1 is the neutral gravitational point between Earth and Sun where a satellite can maintain position with minimal fuel while measuring the undisturbed solar wind before it reaches Earth.
Question 6: Solar wind density enhancements called 'heliospheric plasma sheets' crossings are associated with:
- Increased solar energetic particle flux
- Sector boundary crossings of the heliospheric current sheet, linked to enhanced geomagnetic activity (Correct answer)
- Elevated cosmic ray flux at Earth
- High-speed stream interfaces only
Correct answer: Sector boundary crossings of the heliospheric current sheet, linked to enhanced geomagnetic activity
The heliospheric current sheet separates magnetic sectors of opposing polarity; crossings are often accompanied by density enhancements and can trigger weak geomagnetic activity.
SWP Solar Wind & Interplanetary Medium 1
The Parker spiral describes: